PROJECT SUMMARY/ABSTRACT Identifying successful methods for reducing long-term energy intake continues to be a challenge in obesity treatment. Basic behavioral research has found that the rate of habituation (i.e., rate of reduction in physiological and behavioral responding) to food is related to amount of food consumed, and faster habituation rates reduce food intake. The rate of habituation to food can be accelerated when variety in foods is limited, producing decreased intake. Thus, a dietary prescription that limits variety of high-energy-dense (RED) foods may boost ability to reduce long-term energy intake, enhancing long-term weight loss. Furthermore, habituation rates to food show large individual variability. Individuals with overweight habituate slower to food than individuals with a healthy weight, and slower habituation rates predict greater increases in child standardized body mass index. Thus, slower habituation rates to food may be a behavioral phenotype for increased risk of suboptimal weight outcomes. Obesity interventions that accelerate habituation to food may then be more beneficial for those with this behavioral phenotype. We have been conducting a line of translational research that applies habituation theory to obesity treatment, involving: 1) studies systematically testing basic concepts to better inform intervention development; 2) ?proof-of-concept? testing; and 3) efficacy trials. The long-term goal is to develop a dietary prescription that harnesses habituation as a mechanism for reducing long-term energy intake. We have piloted a limited variety prescription (limited variety of RED foods) within a 6-month family-based behavioral obesity treatment (FBT) for children. Twenty-four families, with a child > 85th percentile body mass index (BMI) and aged 8 to 12 years, were randomized to FBT or to FBT that included a limited dietary variety prescription (FBT+Variety). At 6-months children in FBT+Variety had a significantly greater reduction in percent overweight than those in FBT (?15.4% vs.? 8.9%). Research is needed to examine if limiting variety improves long-term weight loss, if this improvement is due to enhanced habituation, and explore if there is a behavioral phenotype that more greatly benefits from this dietary approach. We plan to implement a novel limited food variety prescription within a 24-month FBT to examine its effect on 24-month BMI. One hundred fifty-six children aged 8 to 12 years at > 85th percentile BMI will be randomized to one of two, 24- month interventions compared in our 6-month pilot study: FBT or FBT+Variety. Child and adult caregiver assessments will occur at 0, 6, 12, 18, and 24 months on anthropometrics, dietary intake, and habituation. We will determine: 1) the influence of FBT+Variety on long-term weight loss; and 2) the influence of FBT+Variety on long-term habituation and if habituation rate mediates differences in dietary intake and BMI between conditions. We will explore if the behavioral phenotype can be used to identify who benefits most from the limited variety prescription to better individualize treatment (?precision medicine?).